1. Field of the Invention
The present invention is a separation vessel for separating gas, sediment, and water from crude oil for oil production that contains significant amounts of water.
2. Description of the Related Art
With oil prices hovering around $85-$100/barrel, current economics strongly favor separating and selling every drop of crude oil possible. Water production now dominates many oilfield operations, and too much oil remains entrained in it. The conventional API gun barrel separator tanks are the type of separation vessels that are often used to try to separate that oil. Those tanks were designed to remove small quantities of water from large quantities of oil, not small amounts of oil from large quantities of water. Today's high water cuts suggest that these old industry workhorses may be obsolete when large volumes of water are involved.
The present invention addresses this problem with a more sophisticated, a more complex, and a more expensive type of separator. However, at today's oil prices, the initial cost of installation of this more expensive type of separator is recovered in just a matter of days by the direct benefit of increased oil recovery achieved by this new separator design over the conventional gunbarrel vessels currently in use.
Also, there are other indirect cost savings associated with disposal of water effluent from the present invention verses disposal of water effluent from the conventional gun barrel vessel tanks currently in use. The oil that exits with the water effluent from the inefficient conventional gunbarrel vessels is disposed of with the water effluent into injection wells or disposal wells. The oil contained in that water effluent has a tendency to plate out on the tubular, the well liner, the well bore and the formation rock of the disposal well. Because the oil is water-insoluble, as it coats the formation face, it begins to restrict or plug the flow of water flowing from the well to the formation. Most of the suspended solids in the water accumulate in this oily material, increasing the volume of the deposit and causing even more plugging. This oily residue tends to build up in the formation within a few feet of the well bore and on the formation face, forming impervious flow paths that eventually cause injection pressures to climb and injection rates to decline.
As injection rates decline, it is common practice to stimulate the disposal well, often using a dilute solution of hydrochloric acid or other common stimulation solvents, usually with added surface active chemical ingredients. After the first stimulation, the result is that the well is returned to near its original injection rate and pressure. However, it is also common that after the first stimulation, injection rates fall off and injection pressures increase more rapidly than before. This situation becomes more severe after each subsequent stimulation effort until a point of diminishing returns is reached. Eventually, when stimulation efforts fail and the disposal well bore is obviously damaged beyond reclamation, it is then necessary to re-drill, sidetrack and recomplete the existing disposal well, or to drill a new disposal well. The costs for these more drastic measures range from $500,000 to $3,000,000. This is the indirect cost of poor water quality in the effluent from the oil water separators that are in use today.
With such staggering direct and indirect costs, it seems prudent to take positive steps to capture and sell as much of the entrained oil as possible in the crude oil stream, and to take steps to prevent well plugging from any and all other sources of contaminants such as solids, bacteria, etc.
One step is to select oil-water separation equipment that actually separates all physically separable oil from the produced water. The goal of the present invention is to provide a 20-30 fold increase in separation efficiency over conventional gunbarrel separating tanks. Conventional gunbarrel tanks will be only 3-5% hydraulically efficient at separating entrained oil, whereas the present invention is 60-72% hydraulically efficient at separating the entrained oil. The present invention reduces the oil concentration to below 50 ppm in the effluent water as compared to approximately 300-1500 ppm of oil in the effluent water emanating from conventional gunbarrel separation tanks.